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-rw-r--r--examples/test-session.cpp17
1 files changed, 9 insertions, 8 deletions
diff --git a/examples/test-session.cpp b/examples/test-session.cpp
index 1a53c66..97d5754 100644
--- a/examples/test-session.cpp
+++ b/examples/test-session.cpp
@@ -759,7 +759,8 @@ void cmd_board_info(void) { // TODO print more information
// -- Helper functions --------------------------------------------------------
void measure_adc_noise(uint8 pin) {
- uint16 data[100];
+ const int N = 1000;
+ uint16 x;
float mean = 0;
float delta = 0;
float M2 = 0;
@@ -767,21 +768,21 @@ void measure_adc_noise(uint8 pin) {
// Variance algorithm from Welford, via Knuth, by way of Wikipedia:
// http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#On-line_algorithm
- for (int i = 0; i < 100; i++) {
- data[i] = analogRead(pin);
- delta = data[i] - mean;
- mean = mean + delta / (i + 1);
- M2 = M2 + delta * (data[i] - mean);
+ for (int i = 1; i <= N; i++) {
+ x = analogRead(pin);
+ delta = x - mean;
+ mean += delta / i;
+ M2 = M2 + delta * (x - mean);
}
SerialUSB.print("header: D");
SerialUSB.print(pin, DEC);
SerialUSB.print("\tn: ");
- SerialUSB.print(100, DEC);
+ SerialUSB.print(N, DEC);
SerialUSB.print("\tmean: ");
SerialUSB.print(mean);
SerialUSB.print("\tvariance: ");
- SerialUSB.println(M2 / 99.0);
+ SerialUSB.println(M2 / (float)(N-1));
pinMode(pin, OUTPUT);
}